Abstract:

Minimally invasive methods and devices for introducing a spinal fixation
element into a surgical site in a patient's spinal column are provided.
In one embodiment, a dissection tool is provided for separating muscles
along a muscle plane without causing damage to the muscles. The
dissection tool can also include a lumen extending therethrough for
receiving a guide wire. The tool allows the guide wire to be positioned
relative to a vertebra, and once properly positioned, the tool can be
removed to allow a spinal anchor to be delivered along the guide wire and
implanted into the vertebra.

Claims:

1. A minimally invasive surgical method, comprising:forming an incision
through tissue located adjacent to a vertebra in a patient's spinal
column;identifying a muscle plane;inserting a substantially planar blunt
tip of a tool through the incision while manipulating the blunt tip along
the muscle plane extending between the incision and the vertebra to
separate the muscles.

2. The method of claim 1, wherein the longissimus thoracis and multifidus
muscles are separated.

3. The method of claim 1, wherein the incision is a minimally invasive
percutaneous incision.

4. The method of claim 1, further comprising inserting a guide wire
through a lumen extending through the tool.

5. The method of claim 4, wherein the guide wire extends into the
vertebra.

6. The method of claim 4, further comprising removing the tool from the
guide wire such that the guide wire extends between the incision and the
vertebra.

7. The method of claim 6, further comprising delivering a spinal anchor
along the guide wire and implanting the spinal anchor in the vertebra.

8. The method of claim 6, further comprising inserting a plurality of
dilators over the guide wire to dilate tissue surrounding the guide wire.

9. The method of claim 8, further comprising inserting a cannula over the
plurality of dilators and removing the dilators.

10. The method of claim 9, further comprising delivering a spinal anchor
through the cannula.

11. A minimally invasive surgical method, comprising:making a first
incision in a patient;inserting a blunt tip of a tool through the first
incision and manipulating the blunt tip to create a first pathway from
the first incision, between a muscle plane, to a first site on a first
vertebral body;advancing a guide wire through the tool to position a
distal end of the guide wire adjacent the first site.

12. The method of claim 11, further comprising removing the tool and
advancing a first implant along the guide wire to the first site on the
first vertebral body.

13. The method of claim 12, further comprising placing a fixation element
through the first pathway in an orientation substantially parallel to a
longitudinal axis of the first pathway, and coupling a portion of the
fixation element to the first anchor.

14. The method of claim 11, further comprising:making a second incision in
a patient;inserting a blunt tip of a tool through the second incision and
manipulating the tool to create a second pathway from the second
incision, between a muscle plane, to a second site on a second vertebral
body; andadvancing a guide wire through the tool to position a distal end
of the guide wire adjacent to the second site.

15. The method of claim 14, further comprising removing the tool and
advancing a second implant along the second pathway to the second site on
the second vertebral body.

16. The method of claim 15, further comprising placing a fixation element
through the first pathway and coupling a portion of the fixation element
to the first and second implants.

17. The method of claim 16, wherein the fixation element is inserted
through the first pathway in an orientation substantially parallel to a
longitudinal axis of the first pathway.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]The present application is a continuation of U.S. patent application
Ser. No. 10/711,704 filed on Sep. 30, 2004 and entitled "Methods and
Devices for Spinal Fixation Element Placement," now U.S. Pat. No. ______,
which is a continuation-in-part of U.S. patent application Ser. No.
10/738,130 filed on Dec. 16, 2003 and entitled "Methods and Devices for
Spinal Fixation Element Placement," now U.S. Pat. No. 7,527,638. These
references are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

[0002]This application relates to tools for use in spinal surgery, and in
particular to minimally invasive methods and devices for introducing a
spinal fixation element to one or more spinal anchor sites within a
patient's spine.

BACKGROUND OF THE INVENTION

[0003]For a number of known reasons, spinal fixation devices are used in
orthopedic surgery to align and/or fix a desired relationship between
adjacent vertebral bodies. Such devices typically include a spinal
fixation element, such as a relatively rigid fixation rod, that is
coupled to adjacent vertebrae by attaching the element to various
anchoring devices, such as hooks, bolts, wires, or screws. The fixation
elements can have a predetermined contour that has been designed
according to the properties of the target implantation site, and once
installed, the instrument holds the vertebrae in a desired spatial
relationship, either until desired healing or spinal fusion has taken
place, or for some longer period of time.

[0004]Spinal fixation elements can be anchored to specific portions of the
vertebrae. Since each vertebra varies in shape and size, a variety of
anchoring devices have been developed to facilitate engagement of a
particular portion of the bone. Pedicle screw assemblies, for example,
have a shape and size that is configured to engage pedicle bone. Such
screws typically include a threaded shank that is adapted to be threaded
into a vertebra, and a head portion having a rod-receiving element,
usually in the form of a U-shaped slot formed in the head. A set-screw,
plug, or similar type of fastening mechanism is used to lock the fixation
element, e.g., a spinal rod, into the rod-receiving head of the pedicle
screw. In use, the shank portion of each screw is threaded into a
vertebra, and once properly positioned, a rod is seated through the
rod-receiving member of each screw and the rod is locked in place by
tightening a cap or other fastener mechanism to securely interconnect
each screw and the fixation rod.

[0005]Recently, the trend in spinal surgery has been moving toward
providing minimally invasive devices and methods for implanting spinal
fixation devices. One such method, for example, is disclosed in U.S. Pat.
No. 6,530,929 of Justis et al. and it utilizes two percutaneous access
devices for implanting an anchoring device, such as a spinal screw, into
adjacent vertebrae. A spinal rod is then introduced through a third
incision a distance apart from the percutaneous access sites, and the rod
is transversely moved into the rod-engaging portion of each spinal screw.
The percutaneous access devices can then be used to apply closure
mechanisms to the rod-engaging heads to lock the rod therein. While this
procedure offers advantages over prior art invasive techniques, the
transverse introduction of the rod can cause significant damage to
surrounding tissue and muscle. Moreover, the use of three separate access
sites can undesirably lengthen the surgical procedure, and increase
patient trauma and recovery time.

[0006]Accordingly, there remains a need for improved minimally invasive
devices and methods for introducing a spinal fixation element into a
patient's spine.

SUMMARY OF THE INVENTION

[0007]Disclosed herein are minimally invasive methods and devices for
delivering a spinal fixation element to one or more spinal anchor sites
in a patient's spinal column. In one embodiment, a minimally invasive
surgical method is provided that includes forming an incision through
tissue located adjacent to a vertebra in a patient's spinal column, and
inserting a blunt tip of a tool through the incision while manipulating
the tool along the muscle plane extending between the incision and the
vertebra to separate the muscles. The blunt tip preferably has a
substantially planar configuration, or it includes at least one surface
that is substantially planar. In an exemplary embodiment, the blunt tip
of the tool is adapted to separate the longissimus thoracis and
multifidus muscles. The method can also include inserting a guide wire
through a lumen extending through the tool. The guide wire is preferably
positioned such that it extends into the vertebra. Once properly
positioned, the tool can be removed leaving the guide wire in position to
receive a spinal implant, such as a spinal anchor, which is preferably
delivered to the vertebra along the guide wire. The aforementioned method
can be repeated to deliver one or more additional implants to adjacent
vertebrae. A spinal fixation element, such as a spinal rod, can then be
delivered along one of the pathways extending to a vertebral body, and it
can be coupled to the implant implanted within the adjacent vertebrae. In
an exemplary embodiment, the fixation element may be inserted through one
of the pathways in an orientation substantially parallel to a
longitudinal axis of the first pathway. In certain exemplary embodiments,
the spinal fixation element may be delivered through a cannula that
extends along the pathway from the tissue surface to one of the vertebra.

[0008]In another exemplary embodiment, a medical device kit for use in
spinal surgery may include a tissue dissection tool have a blunt member
formed on a distal end thereof and adapted to separate muscles along a
muscle plane without causing damage to the muscles. The exemplary tissue
dissection tool may include a lumen extending therethrough. The kit may
also include at least one guide wire that is adapted to be disposed
through the lumen in the tissue dissection tool, and at least one spinal
anchor that is adapted to be implanted in a vertebral body. The kit can
may also include at least one cannula that is adapted to provide a
pathway from a tissue surface to a vertebral body for delivering a spinal
anchor to the vertebral body, and/or at least one spinal fixation element
that is adapted to couple to and extend between at least two spinal
anchors.

[0009]In yet another embodiment of the present invention, a spinal anchor
is percutaneously delivered to a vertebral body having a percutaneous
access device mated thereto and having a lumen extending therethrough and
defining a longitudinal axis. A spinal fixation element is then advanced
through the lumen in the percutaneous access device in a first,
lengthwise orientation in which the fixation element is substantially
parallel to the longitudinal axis of the percutaneous access device. The
spinal fixation element can then be manipulated to extend in a second
orientation, such that the fixation element is angled with respect to the
first orientation, to position the spinal fixation element in relation to
the spinal anchor. The method can also include the step of percutaneously
delivering a second spinal anchor to a vertebral body with a second
percutaneous access device mated thereto. The spinal fixation element
thus preferably extends between the first and second spinal anchors in
the second orientation.

[0010]In an exemplary embodiment, the percutaneous access device is in the
form of an elongate, generally cylindrical tube that is adapted for
percutaneous delivery and that is adapted to mate to a spinal anchor. The
tube can include proximal and distal ends with a lumen extending
therebetween. The lumen is adapted to transport a spinal fixation element
therethrough in a first, lengthwise orientation that is substantially
parallel to a longitudinal axis of the percutaneous access device, and to
deliver the spinal fixation element to a spinal anchor site in a second
orientation that is angled with respect to the first orientation, and
more preferably that is substantially parallel to a patient's spinal
column. The percutaneous access device can also include at least one
sidewall opening extending from the distal end of the elongate, generally
cylindrical tube through at least a portion thereof for facilitating
transition of a spinal fixation element from the first orientation to the
second orientation. In one embodiment, the device includes opposed
sidewall openings formed therein adjacent to the distal end thereof. The
device can also optionally or alternatively include a guide member formed
within the lumen that is adapted to direct a spinal fixation element
disposed therein from the first orientation to the second orientation.
The guide member can be, for example, a sloped shelf formed within the
lumen of the percutaneous access device.

[0011]In another embodiment of the present invention, a minimally invasive
method for delivering a spinal fixation element to a spinal anchor site
in a patient's spinal column is provided. The method includes the step of
introducing a spinal fixation element into a lumen of a percutaneous
access device. The lumen preferably forms a pathway to a spinal anchor
disposed in a patient's vertebra. In an exemplary embodiment, the
percutaneous access device has an outer diameter that is substantially
the same as or less than a largest width of the spinal anchor to which it
is attached. A person skilled in the art will appreciate that the outer
diameter of the percutaneous access device can optionally be greater than
the outer diameter of the spinal anchor to which it is attached. The
method further includes the steps of advancing the spinal fixation
element distally through the lumen in a first, lengthwise orientation
that is substantially parallel to a longitudinal axis of the percutaneous
access device, and manipulating the spinal fixation element into a second
orientation that is substantially parallel to the patient's spinal
column. The spinal fixation element can then be positioned relative to
one or more spinal anchors.

[0012]In other aspects of the present invention, a minimally invasive
surgical method is provided that includes the steps of making a first
percutaneous incision in a patient, and creating a first pathway from the
first percutaneous incision to an anchor site on a first vertebral body.
Preferably, the pathway is a minimally invasive pathway such that it
leads only to a single anchor site, rather than multiple anchor sites.
This can be achieved, for example, by a percutaneous access device that
has a substantially uniform width from the first percutaneous incision to
a first anchor site on a first vertebral body. In an exemplary
embodiment, the first pathway has a width that is substantially equal to
or less than a width of the first percutaneous incision, and/or that is
substantially equal to or less than a width of a first anchor. The method
also includes the steps of placing a first anchor through the first
percutaneous incision, advancing the first anchor along the first pathway
to the single anchor site, and placing a fixation element through the
first pathway in an orientation substantially parallel to a longitudinal
axis of the first pathway.

[0013]In a further embodiment, a second percutaneous incision can be made
in a patient, and a second minimally invasive pathway can be created from
the second percutaneous incision to a second anchor site on a second
vertebral body. A second anchor is then advanced along the second pathway
to the second anchor site on the second vertebral body.

[0014]Additional methods and devices for introducing a spinal fixation
element to one or more spinal anchor sites are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view of a percutaneous access device coupled
to an anchor according to one embodiment of the present invention;

[0016]FIG. 2 is a cross-sectional view taken along the longitudinal axis
of the percutaneous access device shown in FIG. 1;

[0017]FIG. 3A is a partially cut-away view of another embodiment of a
percutaneous access device having a guide member formed therein;

[0018]FIG. 3B is a partially cut-away view of the percutaneous access
device shown in FIG. 3A having a sleeve disposed there around and a
spinal anchor mated thereto;

[0019]FIG. 4A is a posterior view of three percutaneous incisions formed
in the thoracolumbar fascia of a patient's back;

[0020]FIG. 4B is a posterior view of six percutaneous incisions formed in
the thoracolumbar fascia of a patient's back;

[0021]FIG. 5A is an end view showing a blunt dissection of the muscles
surrounding a patient's vertebra;

[0022]FIG. 5B is an end view of the vertebra shown in FIG. 5A showing a
technique using a finger for separating the muscles along the dissected
muscle plane to gain access to the vertebra;

[0023]FIG. 5c is an end view of the vertebra shown in FIG. 5A showing
another embodiment of a technique using a tool for separating the muscles
along the dissected muscle plane to gain access to the vertebra;

[0024]FIG. 5D is an end view of the vertebra shown in FIG. 5c showing the
tool further inserted along the dissected muscle plane;

[0025]FIG. 5E is an end view of the vertebra shown in FIG. 5c showing
placement of a guide wire through the tool and into the patient's
vertebra;

[0027]FIG. 5G is a cross-sectional view of the tool shown in FIG. 5F taken
along line A-A;

[0028]FIG. 6 is an end view of the vertebra shown in FIG. 4 showing
placement of a guide wire through the incision and into the patient's
vertebra;

[0029]FIG. 7 is an end view of the vertebra shown in FIG. 6 having an
obturator and several dilators disposed over the guide wire to dilate the
tissue and muscles;

[0030]FIG. 8 is perspective view of a first spinal anchor implanted in a
vertebra and having a percutaneous access device coupled thereto and
extending through a percutaneous incision formed in the patient's tissue
surface, and a second spinal anchor being implanted into an adjacent
vertebra and having a percutaneous access device coupled thereto with a
driver tool extending therethrough;

[0031]FIG. 9 is a perspective view of two percutaneous access devices
attached to spinal anchors that are disposed within adjacent vertebrae in
a patient's spinal column;

[0032]FIG. 10 illustrates a method for introducing a spinal fixation
element through a partially cut-away view of one of the percutaneous
access devices shown in FIG. 9;

[0033]FIG. 11 is a perspective view of the spinal fixation element shown
in FIG. 10 being advanced in toward the spinal anchors using a pusher
device;

[0034]FIG. 12 is a perspective view of the spinal fixation element shown
in FIG. 11 after it is fully positioned within receiver heads of the
adjacent spinal anchors;

[0035]FIG. 13 illustrates a method for introducing a spinal fixation
element through a partially cut-away view of the percutaneous access
device shown in FIGS. 3A and 3B;

[0036]FIG. 14 is a perspective view of the spinal fixation element shown
in FIG. 13 being advanced toward the spinal anchors using a pusher
device;

[0037]FIG. 15 is a perspective view of the spinal fixation element shown
in FIG. 14 advanced further toward the receiver heads of the adjacent
spinal anchors;

[0038]FIG. 16 is a perspective view of the spinal fixation element shown
in FIG. 15 about to be disposed within the receiver heads of the adjacent
spinal anchors; and

[0039]FIG. 17 is a perspective view of a compression tool positioned
around the percutaneous access devices shown in FIG. 12 and compressing
the devices toward one another, and a closure mechanism being applied
through one of the percutaneous access devices to lock the spinal
fixation element in relation to the spinal anchor.

DETAILED DESCRIPTION OF THE INVENTION

[0040]The present invention provides minimally invasive methods and
devices for introducing a spinal fixation element into a surgical site in
a patient's spinal column. In general, the method involves advancing a
spinal fixation element in a lengthwise orientation along a minimally
invasive pathway that extends from a minimally invasive percutaneous
incision to a spinal anchor site. In an exemplary embodiment, a
percutaneous access device is used to create the minimally invasive
pathway for receiving the spinal fixation element and for delivering the
fixation element to a spinal anchor site. The spinal fixation element is
preferably inserted through a lumen in the percutaneous access device in
a lengthwise orientation, such that the spinal fixation element is
oriented substantially parallel to a longitudinal axis of the
percutaneous access device. As the spinal fixation element approaches or
reaches the distal end of the pathway, the spinal fixation element can be
manipulated to orient it at a desired angle with respect to the
percutaneous access device, preferably such that the spinal fixation
element is substantially parallel to the patient's spinal column. The
spinal fixation element can then optionally be positioned to couple it,
either directly or indirectly, to one or more spinal anchors. A fastening
element or other closure mechanism, if necessary, can then be introduced
into the spinal anchor site to fixedly mate the spinal fixation element
to the anchor(s).

[0041]The methods and devices of the present invention are particularly
advantageous in that they can be achieved using one or more minimally
invasive percutaneous incisions for accessing the spinal column. Such
incisions minimize damage to intervening tissues, and they reduce
recovery time and post-operative pain. The present invention also
advantageously provides techniques for delivering spinal fixation
elements and anchors along a minimally invasive pathway, thus eliminating
the need to create a large working area at the surgical site.

[0042]While a variety of devices can be used to perform the methods of the
present invention, FIGS. 1 and 2 illustrate an exemplary embodiment of a
percutaneous access device 12 that is mated to a spinal anchor 50 (FIG.
1) to form a spinal implant assembly 10. As shown, the device 12 is in
the form of a generally elongate, cylindrical tube having an inner lumen
12c formed therein and defining a longitudinal axis L that extends
between proximal and distal ends 12a, 12b. The size of the access device
12 can vary depending on the intended use, but it should have a length l
that allows the proximal end 12a of the access device 12 to be positioned
outside the patient's body, while the distal end 12b of the access device
12 is coupled to, or positioned adjacent to, a spinal anchor, e.g.,
anchor 50, that is disposed in a vertebra in a patient's spine. The
access device 12 is also preferably adapted to provide a minimally
invasive pathway for the delivery of a spinal fixation element, and in
particular, the percutaneous access device 12 should also be adapted to
be implanted through a minimally invasive percutaneous incision, which is
a relatively small incision that typically has a length that is less than
a diameter or width of the device being inserted therethrough.

[0043]In an exemplary embodiment, the device 12 has an inner diameter
di that is sufficient to allow a spinal fixation element to be
introduced therethrough, preferably in a lengthwise orientation. The
inner diameter di can also optionally be configured to allow a
driver mechanism to be introduced therethrough for applying a closure
mechanism to lock the spinal fixation element in relation to a spinal
anchor. The outer diameter do of the access device 12 can also vary,
and it can be the same as, less than, or greater than an outer diameter
dr of the spinal anchor. In the illustrated embodiment, the access
device 12 has an outer diameter do that is substantially the same as
an outer diameter dr of the spinal anchor, which, as illustrated in
FIG. 1, is the receiver head 52 of a spinal screw 50. This is
particularly advantageous in that the size of the incision does not need
to be any larger than necessary. The matching outer diameters do,
dr of the access device 12 and the anchor 50 also allow the access
device 12 and/or the anchor 50 to be introduced through a cannula. If the
access device 12 is mated to the anchor 50, the matching outer diameters
do, dr also allows a sleeve or other device to be slidably
disposed there around to prevent disengagement between the access device
12 and the anchor 50. In another, exemplary embodiment, the outer
diameter do of the access device 12 can be slightly greater than the
outer diameter dr of the spinal anchor. By way of non-limiting
example, where a receiver head of the spinal anchor has an outer diameter
dr that is about 13 mm, the access device 12 preferably has an outer
diameter do that is about 15 mm.

[0044]The percutaneous access device 12 also preferably includes at least
one sidewall opening or slot 14 formed therein, and more preferably it
includes two opposed sidewall openings (only one opening 14 is shown)
formed therein and extending proximally from the distal end 12b thereof.
The openings 14 allow a spinal fixation element to be introduced through
the device 12 in a first, lengthwise orientation, in which the spinal
fixation element is substantially parallel to the longitudinal axis L of
the access device 12. The spinal fixation element can then to be
manipulated to extend at an angle with respect to the first orientation,
such that the fixation element extends in a direction substantially
transverse to the longitudinal axis L of the access device 12, for
example, in a direction that is substantially parallel to the patient's
spine. Since the length L of the spinal fixation element will necessarily
be greater than the inner diameter di of the access device 12, the
openings 14 allow the spinal fixation element to pass therethrough while
being transitioned from the first, lengthwise orientation to the second
orientation. A person skilled in the art will appreciate that the exact
position of the spinal fixation element with respect to the longitudinal
axis L will of course vary depending on the configuration of the spinal
fixation element.

[0045]The shape and size of each opening 14 can vary, but the opening(s)
14 should be effective to allow movement of the spinal fixation element
from the first orientation to the second orientation. In an exemplary
embodiment, the openings 14 extend over about half of the length, or less
than half of the length, of the percutaneous access device 12. The shape
of each slot 14 can be generally elongate, and they should each have a
width w that is sufficient to accommodate the diameter of the spinal
fixation element. A person skilled in the art will appreciate that the
percutaneous access device 12 can include any number of sidewall openings
having any shape that is sufficient to allow a spinal fixation element to
be moved from the first orientation to the second orientation.

[0046]In another embodiment of the present invention, shown in FIGS.
3A-3B, the percutaneous access device 112 can also optionally include a
guide member 120 formed within the distal end 112b of the lumen 112c to
help guide the spinal fixation element from the first orientation to the
second orientation. The guide member 120 can have a variety of
configurations, but it should be effective to guide the spinal fixation
element from the first orientation toward the anchor 50 attached to, or
positioned adjacent to, the access device 112, and optionally toward
anchor(s) implanted in adjacent vertebrae. In an exemplary embodiment, as
shown, the guide member 120 is in the form of a sloped shelf formed
within the inner lumen 112c of the access device 112 and preferably
positioned opposite to a single sidewall slot 114 formed in the access
device 112. The sloped shelf 120 can vary in shape and size depending on
the type of fixation element being used and/or the geometry of the access
device. In use, as the leading end of a spinal fixation element, such as
a spinal rod, contacts the shelf 120, the shelf 120 begins to direct the
spinal fixation element into the second orientation, thereby causing the
spinal fixation element to extend in a direction that is substantially
transverse to the axis L of the device 112, and that is preferably
substantially parallel to the patient's spinal column. The spinal
fixation element can then be manipulated to position it in relation to
one or more spinal anchors, as will be discussed in more detail below.

[0047]Referring back to FIG. 1, in use, the percutaneous access device 12
can be adapted to attach to a spinal anchor 50. Accordingly, the distal
end 12c of the percutaneous access device 12 can include one or more
mating elements 18 formed thereon or therein for engaging the anchor 50.
Suitable mating elements include, for example, threads, a twist-lock
engagement, a snap-on engagement, or any other technique known in the
art, and in an exemplary embodiment the mating elements are formed on
opposed inner surfaces of the distal end 12b of the access device 12. A
sleeve 100 (partially shown in FIG. 3B) or other device, preferably
having sidewall openings (not shown) that correspond with the sidewall
openings 14 formed in the percutaneous access device 12, can also be
placed over the percutaneous access device 12, and optionally over the
implant 50 as well, to prevent disengagement of the access device 12 from
the implant 50 during use. Exemplary techniques for mating the
percutaneous access device 12 to an anchor are disclosed in a patent
application entitled "Percutaneous Access Devices and Bone Anchor
Assemblies," filed concurrently herewith. A person skilled in the art
will appreciate that a variety of other techniques can be used to
removably mate the percutaneous access device to an anchor.

[0048]For reference purposes, FIG. 1 illustrates an exemplary spinal
anchor for use with the methods and devices of the present invention. A
person skilled in the art will appreciate that a variety of anchors can
be used with the devices and methods of the present invention, including,
for example, spinal screws, hooks, bolts, and wires. FIG. 1 illustrates a
spinal screw that includes a distal, bone-engaging portion, e.g., a
threaded shank 54, and a proximal, U-shaped, receiver head 52 that is
adapted to seat a spinal fixation element, preferably a spinal rod (not
shown). The threaded shank 54 can be fixedly attached to the receiver
head 52 to form a monoaxial screw, or alternatively the shank 54 can be
configured as a polyaxial screw, as shown, that is rotatably disposed
through an opening formed in the distal end of the receiver head 52 to
allow rotation of the shank 54 with respect to the receiver head 52. A
variety of techniques can be used to allow rotation of the head 52 with
respect to the shank 54.

[0049]FIGS. 4A-17 show a minimally invasive method of implanting a spinal
fixation element. While the method is shown and described in connection
with the percutaneous access device 12 and spinal screw 50 disclosed
herein, a person skilled in the art will appreciate that the method is
not limited to use with such devices, and that a variety of other devices
known in the art can be used. Moreover, while only two access devices 12,
12' and two anchors 50, 50' are shown in FIGS. 4-14, the method of the
present invention can be performed using any number of access devices and
anchors. The method can also be performed using only some of the method
steps disclosed herein, and/or using other methods known in the art.

[0050]The procedure preferably begins by forming a minimally invasive
percutaneous incision through the tissue located adjacent to the desired
implant site. While the location, shape, and size of the incision will
depend on the type and quantity of spinal anchors being implanted, FIG.
4A illustrates three midline minimally invasive percutaneous incisions
62a-c formed on one side of three adjacent vertebra in the thoracolumbar
fascia in the patient's back, and FIG. 4B illustrates three additional
midline minimally invasive percutaneous incisions 62d-f formed on the
opposite side of the three adjacent vertebra in the thoracolumbar fascia
in the patient's back. Each incision 62a-f is a stab incision that has a
diameter of about 10-20 mm in diameter, however this can vary depending
on the procedure. In an exemplary embodiment, each incision 62a-f has a
diameter that is equal to or less than a largest diameter of the anchor
and/or the percutaneous access device being inserted therethrough.

[0051]While probably not necessary, once the percutaneous incisions 62a-f
are formed, blunt finger dissection can optionally be used, as shown in
FIG. 5A-5B, to separate the longissimus thoracis and multifidus muscles,
thereby exposing the facet and the junction of the transverse process and
superior articular process.

[0052]FIGS. 5C-5E illustrate another exemplary technique for separating
the longissimus thoracis and multifidus muscles using a blunt tool 200,
which is shown in more detail in FIGS. 5F-5G. Referring first to FIGS.
5F-5G, the tool 200 generally includes a rigid elongate shaft 202 having
proximal and distal ends 202a, 202b. The shaft 202 also includes a lumen
202c extending therethrough between the proximal and distal ends 202a,
202b for receiving a guide wire, such as a k-wire. The lumen 202c may be
sized to receive a guidewire 202c delivered through the lumen 202c. The
proximal end 202a may include a handle 204 formed therein to facilitate
grasping of the tool 200. The handle 204 can have virtually any shape and
size. For example, as shown in FIGS. 5F-5G, the handle 204 in the
exemplary embodiment has a generally elongate cylindrical shape and it
includes ridges 204a formed thereon to facilitate gripping of the device.

[0053]The distal end 202b of the tool 200 includes a blunt member 206
formed thereon. The blunt member 206 may be adapted, e.g., sized and
shaped, to separate muscles along a muscle plane while concomitantly
minimizing trauma to the separated muscles. While the shape of the blunt
member 206 can vary, in an exemplary embodiment, as shown, the blunt
member 206 has a substantially elongate rectangular shape with opposed
front and back surfaces 206a, 206b. The width between the front and back
surfaces 206a, 206b may taper or decreases in a distal direction such
that the distal-most width wb2 is less than the proximal-most width
wb1. Such an exemplary configuration facilitates insertion of the
blunt member 206 between tissue, e.g., muscle, to allow the tissue to be
separated. The width ws extending between opposed side edges of the
front and back surfaces 206a, 206b can also vary, but in an exemplary
embodiment, as shown, the width ws remains constant along the length
of the front and back surfaces 206a, 206b.

[0054]While not shown, the tool 200 can also optionally include an inner
tube disposed within the elongate shaft 202 for preparing the vertebra.
In particular, the inner tube can be slidably disposed within the
elongate shaft 202 to allow the inner tube to be moved distally into bone
to create a divot in the vertebra, thereby preparing the bone for an awl
or tap. The tool 200 can also optionally serve as a drill guide. In
particular, the elongate shaft 202 can have an inner diameter that is
adapted to receive a drill therethrough to guide the drill toward and
into the vertebra. The shaft 202 also serves as a protective cannula for
the drill, inhibiting contact between the drill and the muscles
surrounding the tool 200. A person having ordinary skill in the art will
appreciate that the tool 200 can have a variety of other configurations,
and that the tool 200 can be adapted for a variety of other uses.

[0055]Referring now to FIGS. 5C-5E, the exemplary tool 200 is shown in
use. As shown, after the percutaneous incisions 62a-f are formed, as
previously described, the blunt member 206 of the dissection tool 200 may
be inserted through an incision 62. The incision 62 may be deep enough to
allow the fat layer between the longissimus thoracis and multifidus
muscles to be located. Once located, the tool 200 may be manipulated to
separate or split the longissimus thoracis and multifidus muscles,
thereby exposing the facet and the junction of the transverse process and
superior articular process. Once the tool 200 is positioned adjacent to
or against the vertebra 60, as shown in FIG. 5D, a guide wire, e.g., a
k-wire 64, can be inserted through the lumen 202c in the tool 200 to
position a distal end of the k-wire 64 at or within the vertebra 60, as
shown in FIG. 5E. Fluoroscopy or other imaging may be used to facilitate
proper placement of the k-wire 64. The tool 200 can then be removed from
the k-wire 64, leaving the k-wire 64 to serve as a guide for various
other devices, which will be described in more detail below. This
procedure can be repeated at each incision 62a-f to facilitate placement
of multiple spinal anchors.

[0056]Where tool 200 is not used, a guide wire, e.g., k-wire 64, can be
implanted, either prior to or after formation of the incision, at each
spinal anchor implant site. As shown in FIG. 6, the k-wire 64 preferably
extends between the muscles and into the vertebra at the desired entry
point of the spinal anchor. Fluoroscopy can be used to facilitate proper
placement of the k-wire 64.

[0057]The opposed ends of the incision can then be dilated to provide a
pathway for delivery of a spinal anchor to each implant site. FIG. 7
illustrates dilation at one end of the incision 62 using an obturator 66a
having several dilators 66b, 66c of increasing size placed there over.
The dilators 66b, 66c are delivered over the obturator 66a and k-wire 64
to essentially stretch the skin around the incision 62 and to expand the
pathway to the anchor site.

[0058]Once the incision 62 is dilated to the proper size, an anchor can be
delivered to each anchor site, as shown in FIG. 8. This procedure
typically involves preparation of the vertebra 60 using one or more bone
preparation instruments, such as drills, taps, awls, burrs, probes, etc.
While not always necessary, one or more cannulae can be used to provide a
pathway from the incision 62 to the anchor site for insertion of the bone
preparation instruments and/or the anchor. In an exemplary embodiment, a
relatively small cannula is used to introduce bone preparation
instruments into the surgical site. The incision 62 can then be further
dilated, and the small cannula can be replaced with a larger cannula that
is adapted to receive or mate to the anchor.

[0059]Once the vertebra 60 is prepared, a spinal anchor can be implanted
at each implant site. An access device 12, 12' can be mated to each
anchor 50, 50' after insertion of the anchor 50, 50' into bone 60, 60',
but more preferably each percutaneous access device 12, 12' is attached
to the anchor 50, 50' prior to insertion of the anchor 50, 50' into bone
60, 60' to provide a passageway for a driver tool for driving the anchor
50 into bone 60, 60'. FIG. 8 illustrates anchor 50 implanted in a first
vertebra 60 and having access device 12 attached thereto. While not
shown, the anchor 50 is preferably cannulated to allow the k-wire 64 to
extend through the anchor 50 and the access device 12 to guide the
devices 50, 12 toward the implant site. FIG. 8 further illustrates a
second anchor 50' having an access device 12' mated thereto. As shown,
the screw 50' is about to be implanted in a second vertebra 60' that is
adjacent to the first vertebra 60. Once the screw 50' is positioned
adjacent to the vertebra 60', a driver tool 90 can be positioned through
the access device 12' and coupled to the receiver head 52' of the screw
50' to drive the screw 50' into the vertebra 60'.

[0060]In another embodiment, a sleeve can be placed over each access
device 12, 12', either prior to or after the devices 12, 12', 50, 50' are
implanted, to prevent the devices 12, 12' from becoming disengaged from
the anchors 50, 50' to which they are attached. The sleeve 100, which is
partially illustrated in FIG. 3B, is preferably in the form of a cannula
that has substantially the same configuration as each access device 12,
12'. The use of a sleeve is particularly desirable where the access
devices 12, 12' utilize pin members that engage corresponding detents
formed on an outer surface of each screw head 52, 52', as the sleeve will
prevent the pin members from becoming disengaged from the detents. The
sleeve can also optionally serve as an access device, allowing access
devices 12, 12' to be detached and removed from the anchors 50, 50'.

[0061]After the anchors 50, 50' are implanted, a spinal fixation element
70 is delivered to the anchor site. This can be achieved by introducing
the spinal fixation element 70 through one of the percutaneous access
devices 12, 12' that is attached to the anchor 50, 50', or through some
other percutaneous access device that provides a pathway to the anchor(s)
50, 50'. As shown in FIG. 9, a spinal fixation element, e.g., a spinal
rod 70, is introduced into device 12 in a first, lengthwise orientation,
such that the spinal fixation element 70 is substantially parallel to the
longitudinal axis L of the access device 12. Where the fixation element
has a curved orientation or it has some other configuration, it is
understood that the fixation element is in the "substantially parallel"
orientation when it is positioned lengthwise through the percutaneous
access device.

[0062]The spinal fixation element 70 is then moved distally toward the
distal end 12b of the percutaneous access device 12, as shown in FIGS. 10
and 11. Movement of the spinal fixation element 70 can be achieved using
a manipulator device 80. The manipulator device 80 can have a variety of
configurations, but it should be effective to allow controlled movement
of the fixation element 70. A person skilled in the art will appreciate
that a variety of other techniques can be used to guide the spinal
fixation element 70 through the percutaneous access device 12 and to
position the spinal fixation element 70 in relation to one or more
anchors 50, 50'. Moreover, the spinal fixation element 70 can have a
variety of configurations to facilitate insertion through a percutaneous
access device. By way of non-limiting example, a patent application
entitled "Flexible Spinal Fixation Elements," and filed concurrently
herewith, discloses a spinal fixation element that can be flexed as it is
passed through a percutaneous access device, thereby allowing the spinal
fixation element to transition from the first orientation to the second
orientation. The application also discloses techniques for delivering the
spinal fixation element along a guide wire or cable, thus eliminating the
need for a manipulator device. Other spinal fixation elements suitable
for use with the present invention, in addition to mechanical and
flexible fixation elements, include, for example, inflatable fixation
elements such as those disclosed in U.S. Patent Publication No.
2002/0068975, entitled "Formable Orthopedic Fixation System with Cross
Linking" by Teitelbaum et al., U.S. Patent Publication No. 2002/0082600,
entitled "Formable Orthopedic Fixation System" by Shaolian et al., and
U.S. Patent Publication No. 2002/0198526, entitled "Formed In Place
Fixation System With Thermal Acceleration" by Shaolian et al., each of
which are hereby incorporated by reference in their entirety.

[0063]Referring now to FIGS. 11 and 12, as the spinal fixation element 70
approaches the distal end 12b of the access device 12, the spinal
fixation element 70 can be manipulated to cause the spinal fixation
element 70 to assume a second orientation that is different from the
first orientation, and more preferably that is substantially parallel to
the patient's spinal column and/or transverse to the first orientation.
It is understood that the angle of the fixation element 70 in the second
orientation will vary depending on the type of fixation device being
implanted, as well as the orientation of the access device 12, which can
vary throughout the surgical procedure since the access device 12 can be
positioned at several angles with respect to the patient's spinal column.

[0064]During transition of the spinal fixation element 70 from the first
orientation to the second orientation, a leading end of the spinal
fixation element 70 should be subcutaneously positioned. Where the access
device 12 includes slots or openings (only one opening 14 is shown), the
opening(s) 14 can be used to facilitate movement of the spinal fixation
element 70 into the second orientation as they will allow the spinal
fixation element 70 to extend therethrough during rotation. This may not
be necessary, however, depending on the length of the openings 14, the
length of the spinal fixation element 70, and/or the configuration of the
spinal fixation element 70. As shown in FIGS. 11 and 12, only the leading
end 70a of the spinal fixation element 70 exits the percutaneous access
device 12 through one of the openings 14.

[0065]Referring to FIG. 12, manipulation of the spinal fixation element 70
is continued until the spinal fixation element 70 is positioned in
relation to one or more spinal anchors. Depending on the type of spinal
anchor used, the fixation element can be positioned to be directly or
indirectly mated to the spinal anchor. As shown in FIG. 12, the fixation
element 70 is fully seated in the receiver heads 52, 52' of the adjacent
spinal anchors 50, 50'. The manipulator device 80, if used, can then be
removed from the access device 12.

[0066]In another embodiment, the percutaneous access device 112 shown in
FIGS. 3A and 3B can be used to facilitate introduction of a spinal
fixation element into a surgical anchor site. As previously stated,
access device 112 includes a guide member 20 formed therein to direct the
spinal fixation element 70 from the first orientation to the second
orientation. This is illustrated in FIGS. 13-16. As shown, as the spinal
fixation element 70 is moved distally to come into contact with the guide
member 120, the guide member 120 causes the spinal fixation element 70 to
rotate and extend toward the opening 114 in the percutaneous access
device 112. As a result, the spinal fixation element 70 is directed into
the second orientation, whereby it can be positioned in or adjacent to
the receiver heads 52, 52' of the adjacent spinal implants 50, 50'.

[0067]Referring back to FIG. 12, once the spinal fixation element 70 is
fully seated in the receiver heads 52, 52' of the adjacent spinal anchors
50, 50', the pusher shaft 80, if used, can then be removed or detached
from the spinal fixation element 70, and a closure mechanism can be
applied to one or both receiver heads 52, 52' to retain the spinal
fixation element 70 therein. In an exemplary embodiment, however, a
compression tool 100 is used to compress the access devices 12, 12'
toward one another prior to applying a closure mechanism to each anchor
50, 50'. The closure mechanism(s) can, however, be partially applied
before compression.

[0068]An exemplary compression tool 300 is shown in FIG. 17, and in
general it includes opposed arms 302, 304 that are pivotally coupled to
one another at a substantial mid-point thereof such that each arm 302,
304 includes a distal portion 302b, 304b that is adapted to be disposed
around a percutaneous access device 12, 12', and a proximal, handle
portion 302a, 304a. The device 300 can also include a fulcrum (not shown)
that is disposed between the arms 302, 304 to facilitate controlled
movement of the arms 302, 304 with respect to one another. In use, the
distal portion 302b, 304b of each arm 302, 304 is placed around an access
device 12, 12', preferably around the distal end 12b, 12b' of each device
12, 12' and/or around the head 52, 52' of each anchor 50, 50'. The
proximal, handle portions 302a, 304a are then brought toward one another
to move the access devices 12, 12' toward one another, preferably while
maintaining relative spacing therebetween, as shown in FIG. 17.

[0069]Once properly positioned, a closure mechanism can be applied,
preferably via the access devices 12, 12', to each anchor head 50, 50' to
retain the spinal fixation element 70 within the receiver heads 52, 52'.
A variety of closure mechanisms and tools for delivering closure
mechanisms are known in the art and they can be used with the present
invention. By way of non-limiting example, FIG. 13 illustrates driver
tool 90 disposed through access device 12 for applying a closure
mechanism, such as a set screw, to the receiver head 52 of the spinal
anchor 50 to lock the spinal fixation element 70 with respect to the
spinal anchor 50. This step can be repeated for the adjacent spinal
anchor(s).

[0070]A person skilled in the art will appreciate that the spinal fixation
element 70 does not need to be directly attached to each anchor 50, 50',
and that it can be indirectly attached to the anchors 50, 50' using, for
example, a band clamp, or slotted or offset connectors.

[0071]Once the fixation element 70 is secured in relation to the implants
50, 50', the access devices 12, 12' can be removed from the implants 50,
50', leaving only minimally invasive percutaneous incisions in the
patient where each access device 12, 12' was introduced. This is
particularly advantageous in that it reduces the amount of trauma caused
to the patient, and it minimizes the damage to muscle surrounding the
surgical site.

[0072]As previously stated, a person skilled in the art will appreciate
that the method can be performed in any sequence using any of the steps.
Moreover, the access devices of the present invention can be used to
deliver multiple spinal fixation elements simultaneously or sequentially,
and/or to perform a variety of other surgical procedures not illustrated
or described herein.

[0073]One skilled in the art will appreciate further features and
advantages of the invention based on the above-described embodiments.
Accordingly, the invention is not to be limited by what has been
particularly shown and described, except as indicated by the appended
claims. All publications and references cited herein are expressly
incorporated herein by reference in their entirety.